Caption: Portrait of the French astronomer Urbain Jean Joseph Leverrier, 1811-1877. Leverrier was a student and then a teacher at the Ecole Polytechnique, initially in chemistry and later in astronomy. Realising that the irregularity of the orbit of Uranus was due to the influence of an undiscovered planet (Neptune), he succeeded in computing the mass and orbit of the perturbing body. He sent his prediction of the missing planet's position to Johann Galle in Berlin, who was able to detect it on his first night of looking. It soon became clear that J.C. Adams had made similar predictions some months before.